1. Field of the Invention
The present invention relates to a magnetic data recording apparatus for magnetically recording various items of data on a film by use of a PPM recording method.
2. Related Background Art
A known method of performing a magnetic record on a magnetic medium is a PPM (Pulse Position Modulation) recording method. FIG. 11 illustrates a signal waveform based on the PPM recording method.
According to the PPM recording method, a signal period is fixed at all times, and 0! and 1! are discriminated depending on a difference in terms of a change-of-signal-level position within one period. For instance, 0! indicates that a signal waveform changes in a range from an onset of the signal period to a one-half period position, while 1! indicates that the signal waveform changes after the one-half period position. For example, referring to FIG. 11, 0! indicates that the signal period falls at one-fourth the period from the onset of the signal period (this is referred to as a bit location 25% PPM signal), while 1! indicates that the signal period falls at three-fourths the period from the onset of the signal period (this is referred to as a bit location 75% PPM signal).
With this arrangement, even if a falling position of the signal period deviates to some extent due to a delay, etc. on the data line, the data can be transmitted correctly. That is, referring to FIG. 11, when transmitting the data 0!, and even if the data which is to fall originally in a one-fourth period position from the onset thereof falls with some time-lag due to the delay, etc. on the data line, the data 0! can be recognized on condition that a signal waveform falls within the one-half period. Consequently, a transmission error of the data is hard to occur.
There is known a camera constructed to magnetically record data about photographing such as a date and exposure data, etc. by use of a PPM recording method. In this type of camera, converting the data about the photographing into PPM signals may, it can be considered, involve (1) a software-oriented converting method by use of a CPU or the like incorporated into the camera and (2) a hardware-oriented converting method by providing a PPM signal converting circuit in the interior of the camera. In the case of the (1) method, it is a general practice that a change-of-signal position of the PPM signal is managed by use of a timer. For instance, when outputting 1! of the PPM signal, the timer measures a time from the onset of one period up to 75%. When reaching the 75% position, the signal is switched over from HIGH level to LOW level. When the change-of-signal position is controlled by the timer, however, the CPU is occupied by this processing during an output of the PPM signal, and, meanwhile, other processes are therefore interrupted. Making a preparation for photographing is likely to be time-consuming. For this reason, a CPU exhibiting an excellent processing capability has to be used, and this may be a factor for increasing the costs. On the other hand, in the case of (2) method, a PPM converting circuit has to be provided outwardly of the CPU, resulting in the increment in the costs. At the same time, downsizing of the camera is hindered by an addition of the circuit.
Further, a temperature of a magnetic driving circuit in the magnetic data recording apparatus tends to rise during its operation. If this circuit is composed of an IC, the IC may be damaged due to a rise in the internal temperature thereof.